Bacteriophage: Filamentous Phage Infections: Videos & Practice Problems

Filamentous phages are a type of bacteriophage characterized by their long, fiber-like structure. Unlike other bacteriophages that often lyse the host cell to release new phage particles, filamentous phages do not kill or lyse the bacterial cell. Instead, they cause productive infections where new phages are continuously produced and released through a process called extrusion. This allows the host cell to remain alive, although its growth is inhibited. This non-lytic nature differentiates filamentous phages from lytic phages, which destroy the host cell during the release of new viral particles.

Filamentous phages attach to bacterial cells by specifically binding to the pilus of the host bacterium. The pilus is a hair-like appendage on the surface of the bacterial cell. Once attached, the phage's DNA enters the host cell through the pilus. This process is the initial step in the infection cycle, allowing the phage genome to enter the bacterial cytoplasm where it can begin replication and synthesis of new phage components.

Extrusion is the process by which new filamentous phage particles are released from the host bacterial cell without causing cell lysis. During extrusion, the assembly of new phage particles occurs simultaneously with their release. The phage components, including the viral capsid proteins and replicated DNA, are assembled into new phages, which then exit the cell through the bacterial membrane. This allows the host cell to remain intact and continue producing new phages, although its growth rate is slowed.

Filamentous phages impact their bacterial host cells by inhibiting their growth. Although the host cell is not lysed and remains alive, the continuous production and release of new phage particles through extrusion slow down the cell's growth rate. This can be detrimental to the bacterial cell's overall health and function, even though it is not immediately lethal. The persistent infection can affect the bacterial cell's physiology and its ability to thrive in its environment.

Understanding filamentous phage infections has significant applications in phage therapy and microbial ecology. In phage therapy, filamentous phages can be used to target and control bacterial populations without causing widespread cell lysis, which can be beneficial in treating bacterial infections while minimizing damage to beneficial microbiota. In microbial ecology, studying filamentous phages helps researchers understand the dynamics of bacterial populations and their interactions with phages in natural environments. This knowledge can inform strategies for managing bacterial communities in various settings, including agriculture, industry, and environmental conservation.